Influences of different Zr/Sc ratios on microstructure and mechanical properties of Al-2Si alloy

Abstract The influences of different Zr/Sc ratio on the microstructural evolution and mechanical performances of Al-2Si alloy were investigated in this paper. The as-cast samples were characterized and analyzed by the scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) to indicate the refining effect of the different Zr/Sc ratio on the α-Al and Si phases in Al-2Si alloy. The results indicate that the α-Al phases were refined from coarse dendritic structure to relatively fine equiaxed grains when the Zr/Sc ratio is equal to 1:1. Meanwhile, the eutectic Si phases in Al-2Si-0.2Zr-0.2Sc alloy was modified from the coarse plate and needle to fine fiber and partial granular structure, and the average roundness of eutectic Si was decreased by 75% from 16 to 4. With the refinement of α-Al phases and the modification of eutectic Si structure, the ultimate tensile strength (UTS) was improved by 53% and the elongation (EL) increased by 64% when the Zr/Sc ratio is equal to 1:1. In addition, the UTS decreased and EL enhanced with the increase of tensile temperature. Moreover, the fracture model of Al-2Si-0.2Zr-0.2Sc alloy in 250 °C changed into the ductile fracture.